1. Field of the Invention
The present invention relates to a procedure and apparatus for detecting and counting objects moving at varying speeds within a certain area in which the procedure employs at least one passive detector which detects background radiation.
2. Description of Related Art
The information derived from observing the movements of people or animals can be utilized in various applications. For instance, data obtained by monitoring the movements of people can be used to improve the ability of an elevator control system to quickly respond to different traffic conditions, such as peak traffic. In this case, on the basis of such data, it is possible e.g. to give certain floors a higher priority in the distribution of elevator services or to automatically activate an elevator call in certain circumstances. The movements of people and animals can be detected e.g. by using a Doppler radar, which operates in the microwave range.
In many applications it is preferable to use a simple and cheap passive detector working in the frequency range of either visible light or infrared radiation. Such a detector emits no radiation at all but detects objects on the basis of the signal generated in the detector by the visible light or thermal radiation generated or reflected by the objects.
A passive detector is most useful in cases where the microwave radar can not be used. These cases include applications in which the objects are at a very short distance from the detector, e.g. below 20 cm. Since the passive detector emits no radiation, no safety risks from radiation from the detector are involved and so clearance of the detector by, for example, governmental safety authorities is, at least on that point, substantially assured.
Finnish Patent 73090 presents a solution for counting moving objects, based on the Doppler radar technique. This solution makes use of modern filter banks and thus constitutes a simple and accurate system for counting objects within the operating range of the radars. There are other solutions using the radar technique, but the above-mentioned patent represents the top of the present state of the art.
The drawbacks with radars are the radiation generated and the fact that they can not detect objects at a very close distance. The latter difficulty arises from the limitations of the dynamic range of the radar. If the radar is adjusted for detection of objects within a short distance, then it can not detect farther away from it. Also, the radar always needs both a transmitter and a receiver, resulting in, for example, higher purchase price and installation costs, for the equipment.
There are several solutions for monitoring a given area which make use of harmless background radiation, e.g. visible light, but so far no reasonable solution has been discovered for the detection and counting of moving objects.